The present invention relates to control valves, and in particular an evaporative (EVAP) solenoid control valve having a plunger to open and close a controlled passageway therein and a magnetic flux regulator to regulate the magnetic force applied to the plunger.
It is known in the art of automotive fuel systems to use an evaporative (EVAP) solenoid valve assembly to control the flow of fuel vapor through passage ways connecting a purge canister and an intake manifold. Many control valve assemblies, including EVAP control valve assemblies, are activated by a solenoid assembly supported within the valve. The solenoid assembly, in turn, is actuated in response to a pulse width modulated (PWM) signal generated by the vehicle""s central computer to induce a plunger to open a passageway for the flow of vapor.
The performance of PWM voltage controlled magnetic actuators depends upon the operation temperature and input voltage level. Because automotive operating temperatures can range from approximately xe2x88x9240xc2x0 C. to 150xc2x0 C., and the resistance and current in the coil of the magnetic actuator change with the operating temperature of the vehicle, the magnetic force acting on the valve assembly may vary over 400%.
In present designs the magnetic force has been saturated to reduce the change of the magnetic force on the valve. Although this method has improved the operation of the valve, there still remains a significant variation of the magnetic force on the valve.
The present invention addresses the aforementioned concerns by providing a bypass configuration of the magnetic circuit of the valve assembly. In general the valve assembly includes a valve body defining a chamber with a controlled outlet. A stop and a seat are supported within the chamber of the valve body and are in axial alignment with the controlled outlet. A plunger moves reciprocably between the stop and the seat to open and close the controlled outlet in response to actuation of a solenoid assembly.
The solenoid assembly has a spool supported between a primary and secondary plate and an electromagnetic coil wound about the spool for receiving electrical current and producing a magnetic flux. The magnetic flux has a primary magnetic flux flow path about the electric coil wherein the primary magnetic flux flow path loops through the secondary plate through a sleeve, from the sleeve to the primary plate, through the plunger and the stop and from the stop back through the secondary plate. The solenoid assembly further includes means for providing a secondary bypass magnetic flux flow path for a portion of the magnetic flux. According to one aspect of the invention the means for providing the secondary bypass magnetic flux flow path includes a magnetic flux regulator positioned in the spool for directing a portion of the magnetic flux away from the plunger.
Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.